JP2021120162A - Welding start method of shielded metal arc welding - Google Patents

Abstract

To provide a welding start method of shielded metal arc welding by which both of a skilled worker and an unskilled worker can satisfactorily start welding.SOLUTION: In a welding start method of shielded metal arc welding, a welding current Iw of an initial current value is electrically conducted when a coated electrode comes into contact with a base material, the welding current Iw is increased from the initial current value to a steady-state current value to start welding after lapse of a delay time Td when the coated electrode is pulled up from the base material and arc occurs. The method includes a first welding mode and a second welding mode, and the delay time Td in the second welding mode is set to a value larger than that in the first welding mode. Further, an increasing rate Si of the welding current Iw in the second welding mode is so set to a value smaller than that in the first welding mode. Further, the initial current value changes to a small value over time.SELECTED DRAWING: Figure 2

Description

The present invention relates to a welding initiation method for shielded metal arc welding.

In recent years, there has been an increasing demand for a composite welding power source capable of selectively using consumable electrode type arc welding and non-consumable electrode type arc welding. As the consumable electrode type arc welding, carbon dioxide gas arc welding, MAG welding, MIG welding, shielded metal arc welding and the like are possible. As non-consumable electrode type arc welding, simple TIG welding is possible.

When the main switch of the welding power supply is turned on and the shielded metal arc welding mode is selected as the welding mode, the welding power supply starts to output. In the no-load state where the arc is not ignited, the welding voltage has a maximum voltage value of about 80 to 120 V that can be output by the welding power supply. Since this maximum voltage value is applied between the shielded metal arc welding rod and the base metal, there is a risk of electric shock to the welding operator. For this reason, shielded metal arc welding is provided with an electric shock prevention function that controls the welding voltage in a no-load state to a low value of about 15 V.

In coated arc welding, the welding operator starts welding by bringing the coated welding rod of the welding holder into contact with the base material and pulling it up to ignite the arc, so-called touch start. In this touch start, when the welding worker pulls down the welding holder and the shielded metal arc welding rod comes into contact with the base metal, the welding current of the initial current value is energized, and then the welding worker pulls up the welding holder and the shielded metal arc welding rod becomes the base metal. When an arc is generated apart from the above, the welding current increases from the initial current value to the steady current value after the delay time elapses, and welding is started.

On the other hand, when the welding is finished, the welding holder is pulled up high to generate an arc break.

The invention of Patent Document 1 discloses an arc start method in TIG welding in which an arc is generated by bringing a welding torch provided with a non-consumable electrode at the tip into contact with an object to be welded and pulling it away.

Japanese Unexamined Patent Publication No. 2000-176640

A skilled worker can start welding satisfactorily because the operation of pulling up from the contact of the shielded metal arc welding rod with the base metal is smooth. However, an unskilled worker may not be able to start welding satisfactorily because the operation of pulling up from the contact of the shielded metal arc welding rod with the base metal is not smooth. An unskilled worker may bring the shielded metal arc welding rod into contact with the base metal again immediately after the shielded metal arc welding rod is pulled up and the arc ignites. In such a state, the molten portion at the tip of the shielded metal arc welding rod is welded to the base metal and solidified, resulting in a poor welding start.

Therefore, an object of the present invention is to provide a welding start method for shielded metal arc welding, which enables both skilled and unskilled workers to start welding satisfactorily.

In order to solve the above-mentioned problems, the invention of claim 1 is
When the shielded metal arc welding rod comes into contact with the base metal, the welding current of the initial current value is energized and
In the welding start method of shielded metal arc welding, when the shielded metal arc welding rod is pulled up from the base metal and an arc is generated, the welding current is increased from the initial current value to the steady current value after a delay time elapses to start welding.
It has a first welding mode and a second welding mode.
In the second welding mode, the delay time is set to a larger value than in the first welding mode.
This is a welding start method for shielded metal arc welding.

The invention of claim 2 is
In the second welding mode, the rate of increase of the welding current is set to a smaller value than in the first welding mode.
The welding start method for shielded metal arc welding according to claim 1.

The invention of claim 3 is
The initial current value changes to a small value over time.
The welding start method for shielded metal arc welding according to claim 1 or 2.

According to the present invention, both skilled and unskilled workers can satisfactorily start shielded metal arc welding.

It is a block diagram of the welding power source for carrying out the welding start method of the shielded metal arc welding which concerns on Embodiment 1 of this invention. FIG. 1 is a timing chart of each signal when welding is performed in the welding power supply described above in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
FIG. 1 is a block diagram of a welding power source for carrying out the welding start method of shielded metal arc welding according to the first embodiment of the present invention. The figure shows only the configuration when shielded metal arc welding is performed in the configuration of the composite welding power supply. Hereinafter, each block will be described with reference to the figure.

The main switch SW switches the on / off state of a commercial power source (not shown) such as 3-phase 200V.

When the main switch SW is turned on, the power main circuit PM receives a commercial power supply, performs output control such as inverter control according to a drive signal Dv described later, and outputs a welding current Iw and a welding voltage Vw. Although not shown, the power supply main circuit PM is a primary rectifier circuit that rectifies a commercial power supply, a capacitor that smoothes the rectified DC, and an inverter circuit that converts the smoothed DC into high-frequency AC according to the above drive signal Dv. It is equipped with an inverter transformer that steps down high-frequency AC to a voltage value suitable for arc welding, a secondary rectifier circuit that rectifies the stepped-down high-frequency AC, and a reactor that smoothes the rectified DC.

The welding holder 4 holds the shielded metal arc welding rod 1 and supplies power to the shielded metal arc welding rod 1.

An arc 3 is generated between the shielded metal arc welding rod 1 and the base metal 2. A welding current Iw is energized in the arc 3, and a welding voltage Vw is applied between the shielded metal arc welding rod 1 and the base metal 2. The axial distance of the shielded metal arc welding rod 1 between the tip of the shielded metal arc welding rod 1 and the base metal 2 is the standoff Lw.

The hot start voltage setting circuit VHR outputs a predetermined hot start voltage setting signal Vhr. The value of this hot start voltage setting signal Vhr is set to a large value so as to improve workability during repeated welding in a short cycle. In general, the larger this value, the higher the probability of re-ignition of the arc. On the other hand, the larger this value, the higher the risk of electric shock. Therefore, it is desirable to set the minimum value within the range where the re-ignition of the arc is smooth. If the diameter and / or material of the shielded metal arc welding rod 1 is different, the voltage value at which the arc firing becomes smooth changes. Therefore, it is desirable that the value of the hot start voltage setting signal Vhr is set to an appropriate value according to the diameter and / or material of the shielded metal arc welding rod. The hot start voltage setting signal Vhr is set to, for example, about 60 to 100V.

The electric shock prevention voltage setting circuit VDC outputs a predetermined electric shock prevention voltage setting signal Vdr. Here, Vhr> Vdr. The value of the electric shock prevention voltage setting signal Vdr is set to about 15 V so as to prevent electric shock.

The voltage setting circuit VR receives the above hot start voltage setting signal Vhr, the above electric shock prevention voltage setting signal Vdr, and the hot start period signal Ths described later as inputs, and the hot start period signal Ths is at the High level (hot start period Th). At this time, the value of the hot start voltage setting signal Vhr is output as the voltage setting signal Vr, and when the hot start period signal Ths is at the Low level, the value of the electric shock prevention voltage setting signal Vdr is output as the voltage setting signal Vr.

The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The voltage error amplifier circuit EV receives the above-mentioned voltage setting signal Vr and the above-mentioned voltage detection signal Vd as inputs, amplifies the error of both values, and outputs the voltage error amplification signal Ev.

The current detection circuit ID detects the welding current Iw and outputs the current detection signal Id. The current energization discrimination circuit CD takes the above current detection signal Id as an input, and when this value is equal to or higher than a predetermined current energization discrimination value (about 5A), it determines that the welding current Iw is energized and sets the high level. Outputs the current energization discrimination signal Cd.

The arc discrimination circuit AD receives the above-mentioned current energization discrimination signal Cd and the above-mentioned voltage detection signal Vd as inputs.
When the current energization discrimination signal Cd is the High level (energization) and the voltage detection signal Vd is larger than the predetermined arc discrimination value (about 10V), it is determined that an arc is being generated and the high level is reached.
In other cases, it is determined that the arc is not generated (contact state or no load state), and the arc discrimination signal Ad that becomes the Low level is output.

The welding mode selection circuit MS is a circuit in which a welding operator selects a first welding mode and a second welding mode. When the first welding mode is selected, the level becomes Low, and when the second welding mode is selected, High. The welding mode selection signal Ms, which is the level, is output. The welding mode selection circuit MS is a switch or the like provided on the front panel of the welding power supply. The first welding mode is suitable for a skilled worker's welding start operation, and the second welding mode is suitable for an unskilled worker's welding start operation.

The initial current setting circuit ISR receives the above-mentioned current energization discrimination signal Cd as an input, and when the current energization discrimination signal Cd changes to the High level (energization), it becomes a predetermined initial value, and then the initial current decreases with time. The setting signal Isr is output.

The steady-state current setting circuit ICR outputs a predetermined steady-state current setting signal Icr.

The delay time setting circuit TDR receives the above welding mode selection signal Ms as an input.
When the welding mode selection signal Ms is at the Low level (first welding mode), the predetermined first delay time is set.
When the welding mode selection signal Ms is at the High level (second welding mode), a delay time setting signal Tdr, which is a predetermined second delay time, is output. The second delay time is a value larger than the first delay time.

The increase rate setting circuit SR receives the above welding mode selection signal Ms as an input.
When the welding mode selection signal Ms is at the Low level (first welding mode), the predetermined first increase rate is obtained.
When the welding mode selection signal Ms is at the High level (second welding mode), the increase rate setting signal Sr, which is a predetermined second increase rate, is output. The second increase rate is a value smaller than the first increase rate.

The current setting circuit IR receives the above-mentioned initial current setting signal Isr, the above-mentioned steady-state current setting signal Icr, the above-mentioned delay time setting signal Tdr, the above-mentioned increase rate setting signal Sr, and the above-mentioned arc discrimination signal Ad as inputs.
When the arc discrimination signal Ad is at the Low level (contact state or no load state), the current setting signal Ir, which is the value of the initial current setting signal Isr, is output.
After the delay time Td determined by the delay time setting signal Tdr elapses from the time when the arc discrimination signal Ad changes from the Low level to the High level (arc generation state), it is determined by the increase rate setting signal Sr from the value of the initial current setting signal Isr. When the rate of increase Si increases and the value of the steady-state current setting signal Icr is reached, the current setting signal Ir that maintains that value is output.

The current error amplifier circuit EI receives the above-mentioned current setting signal Ir and the above-mentioned current detection signal Id as inputs, amplifies the error of both values, and outputs the current error amplification signal Ei.

The error amplification circuit EA receives the above-mentioned current error amplification signal Ei, the above-mentioned voltage error amplification signal Ev, and the above-mentioned current energization discrimination signal Cd as inputs, and when the current energization discrimination signal Cd is at the High level (during energization), the current error. The amplification signal Ei is output as an error amplification signal Ea, and when the current energization discrimination signal Cd is at the Low level (non-energized), the voltage error amplification signal Ev is output as an error amplification signal Ea. By this circuit, the welding power source is controlled by a constant current when the welding current Iw is energized, and is controlled by a constant voltage when the welding current is not energized (no load state).

The drive circuit DV receives the above error amplification signal Ea and the prohibition signal Ks described later as inputs, and when the prohibition signal Ks is at the Low level, modulation control is performed by the error amplification signal Ea to output the drive signal Dv, and the prohibition signal Ks is generated. At the high level, the drive signal Dv is not output. Therefore, when the prohibition signal Ks is at the High level, the output from the power supply main circuit PM is stopped.

The reference voltage value setting circuit VTR outputs a predetermined reference voltage value signal Vtr. This reference voltage value signal Vtr has an arc when the pulling distance (standoff Lw) of the shielded metal arc welding rod 1 reaches a desired value according to the value of the current setting signal Ir, the diameter of the shielded metal arc welding rod 1, the material, and the like. Set to extinguish the arc.

The prohibition circuit KS receives the above voltage detection signal Vd and the above reference voltage value signal Vtr as inputs, and the value of the voltage detection signal Vd changes from a state of being less than the value of the reference voltage value signal Vtr to a state of being equal to or higher than that. When the predetermined monitoring period is continued, the prohibition signal Ks which becomes the high level is output only for the predetermined prohibition period. For example, the monitoring period is 100 ms and the prohibition period is 100 ms.

The hot start period circuit THS receives the above prohibition signal Ks as an input, and becomes a high level from the time when the prohibition signal Ks changes from the high level to the low level until the time when the predetermined hot start period Th elapses. Output the signal Ths. This hot start period Th is set in the range of, for example, about 0.5 to 5.0 seconds. This value is set in consideration of the workability of repeated welding in a short cycle.

FIG. 2 is a timing chart of each signal when welding is performed in the welding power supply of FIG. FIG. 3A shows a time change of the welding current Iw, FIG. 3B shows a time change of the welding voltage Vw, FIG. 3C shows a time change of the prohibition signal Ks, and FIG. Shows the time change of the stand-off Lw, FIG. 6 (E) shows the time change of the hot start period signal Ths, and FIG. 6 (F) shows the time change of the arc discrimination signal Ad. The figure shows the time when the welding holder is pulled up during the shielded metal arc welding to end the welding and start the next welding. Hereinafter, the operation of each signal will be described with reference to the figure.

During steady welding before time t1, the standoff Lw, which is the distance between the tip of the shielded metal arc welding rod and the base metal, is maintained substantially constant by the welding operator, as shown in FIG. This stand-off Lw is about 5 mm. During steady welding, as shown in FIG. 1 (A), a constant value welding current Iw determined by the steady current setting signal Icr of FIG. 1 is energized, and as shown in FIG. 1 (B), stand-off Lw (arc) is applied. A substantially constant welding voltage Vw according to the length) is applied. As shown in FIG. 6C, the prohibition signal Ks is at the Low level. Further, as shown in FIG. 6E, the hot start period signal Ths is also at the Low level. As shown in FIG. 6F, the arc discrimination signal Ad has a high level because an arc is generated.

When the welding operator starts the pulling operation of the welding holder to finish the welding from the time t1, the standoff Lw gradually becomes longer as shown in FIG. In response to this, as shown in FIG. 3B, the welding voltage Vw gradually increases. On the other hand, as shown in FIG. 6A, since the welding current Iw is controlled by a constant current, the value before the time t1 is maintained.

At time t2, the welding voltage Vw (voltage detection signal Vd in FIG. 1) shown in FIG. Therefore, as shown in FIG. 6C, the prohibition signal Ks changes to the High level. In response to this, the welding power supply stops the output, so at time t2, the welding current Iw becomes 0A as shown in FIG. 2A, and the welding voltage Vw becomes 0A as shown in FIG. It becomes 0V and the arc is extinguished. When the arc is extinguished, the arc discrimination signal Ad changes to the Low level as shown in FIG. This completes the welding. The monitoring period is about 100 ms, and is provided to prevent chattering in which the prohibition signal Ks repeats the High level / Low level in a short time.

As described above, the reference voltage value is determined by the reference voltage value signal Vtr of FIG. The reference voltage value signal Vtr is set to an appropriate value according to the current setting signal Ir in FIG. 1, the diameter of the shielded metal arc welding rod, the material, and the like. In this way, the standoff Lw at which the arc is extinguished can be made substantially constant, so that workability can be improved.

At time t3, when a predetermined prohibition period elapses from time t2, the prohibition signal Ks returns to the Low level as shown in FIG. In response to this, the welding power supply restarts the output. Since the arc is not ignited in this state, the welding current Iw is not energized and is in a no-load state as shown in FIG. For this purpose, the welding power supply is switched to constant voltage control. When the prohibition signal Ks shown in FIG. 3C changes from the High level to the Low level at time t3, the hot start period signal Ths becomes the High level as shown in FIG. The High level is maintained until the time t4 when the period Th elapses. Therefore, the period from time t3 to t4 is the hot start period Th.

During the hot start period Th at times t3 to t4, the voltage setting signal Vr in FIG. 1 becomes the value of the hot start voltage setting signal Vhr in FIG. Therefore, as shown in FIG. 6B, the welding voltage Vw becomes the hot start voltage value Vwh. The hot start period Th is provided in order to improve the workability of repeated welding in a short cycle.

When the no-load state continues until the time t4, the voltage setting signal Vr in FIG. 1 is switched to the value of the electric shock prevention voltage setting signal Vdr in FIG. Therefore, as shown in FIG. 6B, the welding voltage Vw drops to the electric shock prevention voltage value Vwd. Thereby, electric shock can be prevented.

As the welding operator brings the welding holder closer to the base metal in order to start the next welding from time t5, the standoff Lw gradually becomes shorter as shown in FIG. When the shielded metal arc welding rod comes into contact with the base metal at time t6, as shown in FIG. 1A, the welding current Iw of the initial current value determined by the initial current setting signal Isr of FIG. 1 starts energization. In response to this, the welding power supply is switched to constant current control. As shown in FIG. 3B, the welding voltage Vw is approximately 0V.
The above initial current value is a predetermined initial value (about 20A) at the time of contact at time t6, then decreases with time, and when the predetermined lower limit value (about 10A) is reached, the value is set to time t8. Maintain until the end of the delay period. The initial value of the initial current is set to a small value such that the tip of the shielded metal arc welding rod 1 does not melt so much. The reason why the initial current is reduced with time is to suppress the melting of the tip of the shielded metal arc welding rod 1. This is because if the molten portion becomes large, welding of the shielded metal arc welding rod and the base metal is likely to occur at the time of recontact immediately after the arc is generated, and this is suppressed.

At time t7, when the welder pulls up the weld holder and the tip of the shielded metal arc welding rod separates from the base metal, the arc ignites. In response to this, as shown in FIG. (F), the arc discrimination signal Ad changes to the High level. The delay period is the period from the time when the arc discrimination signal Ad changes to the High level at time t7 to the time t8 when the delay time Td determined by the delay time setting signal Tdr of FIG. 1 elapses. During this delay period, as shown in FIG. 3A, the welding current Iw, which is the above initial current value, continues to be energized. As shown in FIG. 6B, the welding voltage Vw has an arc voltage value of several tens of V. The delay time Td becomes a larger value when the second welding mode is selected than when the first welding mode is selected. For example, the delay time Td is set to 1 ms in the first welding mode and 10 ms in the second welding mote.

When the delay period ends at time t8, as shown in FIG. 1A, the welding current Iw increases at the increase rate Si determined by the increase rate setting signal Sr in FIG. 1, and reaches the above steady-state current value at time t9. When it reaches it, it keeps its value after that. Similarly, as shown in FIG. 3B, the welding voltage Vw also increases to a steady-state voltage value. The rate of increase Si becomes smaller when the second welding mode is selected than when the first welding mode is selected. For example, the rate of increase Si is set to 200 A / ms in the first welding mode and 100 A / ms in the second welding mote.

The welding operator starts pulling up the welding holder at time t7 and stops pulling up around time t9 to maintain an appropriate distance. Correspondingly, as shown in FIG. 3D, the standoff Lw gradually increases from time t7 to 0 mm, and becomes an appropriate value of about 5 mm around time t9. In this way, welding is started.

According to the first embodiment described above, when the shielded metal arc welding rod comes into contact with the base metal, the welding current of the initial current value is energized, and when the shielded metal arc welding rod is pulled up from the base metal and an arc is generated, the welding current is generated after the delay time elapses. In the welding start method of shielded metal arc welding in which welding is started by increasing from the initial current value to the steady current value, a first welding mode and a second welding mode are provided, and in the second welding mode, the first welding mode is used. Set the delay time to a larger value than when. The first welding mode is suitable for the welding start operation of a skilled worker, and the second welding mode is suitable for the welding start operation of an unskilled worker. For skilled workers, the operation of bringing the shielded metal arc welding rod into contact with the base metal once and pulling it up to an appropriate distance is quick and smooth. Therefore, by shortening the delay time described above, it is possible to perform a good welding start in response to a quick operation. For a skilled worker, if the delay time becomes long, the workability at the start of welding deteriorates. An unskilled worker may cause recontact due to camera shake immediately after the shielded metal arc welding rod is brought into contact with the base metal and pulled up to ignite the arc. At this time, if the delay time is long, melting of the tip of the shielded metal arc welding rod is suppressed, so that it is possible to prevent the shielded metal arc welding rod from being welded to the base metal. Therefore, in the present embodiment, both skilled and unskilled workers can start welding satisfactorily.

Further, according to the first embodiment, it is desirable to set the increase rate of the welding current to a smaller value in the second welding mode than in the first welding mode. For skilled workers, the operation of bringing the shielded metal arc welding rod into contact with the base metal once and pulling it up to an appropriate distance is quick and smooth. Therefore, by setting the increase rate of the welding current to a large value, it is possible to perform a good welding start in response to a quick operation. For a skilled worker, when the rate of increase is small, the workability at the start of welding deteriorates. An unskilled worker may cause recontact due to camera shake immediately after the shielded metal arc welding rod is brought into contact with the base metal and pulled up to ignite the arc. At this time, if the rate of increase is small, the melting of the tip of the shielded metal arc welding rod is suppressed, so that the shielded metal arc welding rod can be prevented from being welded to the base metal. Therefore, in the present embodiment, both skilled and unskilled workers can start welding even better.

Further, according to the first embodiment, it is desirable that the initial current value changes to a small value with time. In this way, even if the contact time is long, melting of the tip of the shielded metal arc welding rod can be suppressed, so that welding at the time of recontact can be further prevented.

1 Shielded metal arc welding rod
2 Base material
3 arc
4 Welding holder AD Arc discrimination circuit Ad Arc discrimination signal CD Current current discrimination circuit Cd Current current discrimination signal DV Drive circuit Dv Drive signal EA Error amplification circuit Ea Error amplification signal EI Current error amplification signal Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal ICR steady current setting circuit Icr steady current setting signal ID current detection circuit Id current detection signal IR current setting circuit Ir current setting signal ISR initial current setting circuit Isr initial current setting signal Iw welding current KS prohibition circuit Ks prohibition signal Lw Stand-off MS Welding mode selection circuit Ms Welding mode selection signal PM Power supply Main circuit Si Increase rate SR Increase rate setting circuit Sr Increase rate setting signal SW Main switch Td Delay time TDR Delay time setting circuit Tdr Delay time setting signal Th Hot start period THS hot start period circuit Ths hot start period signal VD voltage detection circuit Vd voltage detection signal VDR electric shock prevention voltage setting circuit Vdr electric shock prevention voltage setting signal VHR hot start voltage setting circuit Vhr hot start voltage setting signal VR voltage setting circuit Vr voltage setting signal VTR Reference voltage value setting circuit Vtr Reference voltage value signal Vw Welding voltage Vwd Electric shock prevention voltage value Vwh Hot start voltage value

Claims (3)

When the shielded metal arc welding rod comes into contact with the base metal, the welding current of the initial current value is energized and
In the welding start method of shielded metal arc welding, when the shielded metal arc welding rod is pulled up from the base metal and an arc is generated, the welding current is increased from the initial current value to the steady current value after a delay time elapses to start welding.
It has a first welding mode and a second welding mode.
In the second welding mode, the delay time is set to a larger value than in the first welding mode.
A method for starting welding of shielded metal arc welding. In the second welding mode, the rate of increase of the welding current is set to a smaller value than in the first welding mode.
The welding start method for shielded metal arc welding according to claim 1. The initial current value changes to a small value over time.
The welding start method for shielded metal arc welding according to claim 1 or 2.

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